WiMAX (Worldwide Interoperability for Microwave Access) is a new technology for wireless packet data communications. WiMAX is similar in concept to wireless local area network (WLAN) technologies defined by IEEE standard 802.11, but has a number of enhancements designed to improve-performance and range. The original WiMAX standard, IEEE 802.16, specified WiMAX in the 10-66 GHz range. More recently, IEEE 802.16a added support for the 2-11 GHz range, and IEEE 802.16e (approved as IEEE 802.16-2005) extended WiMAX to mobile applications, using an enhanced orthogonal frequency division multiple access (OFDMA) modulation scheme. In the context of the present patent application and in the claims, the term “802.16” is used to refer collectively to the original IEEE 802.16 standard and all its variants and extensions, unless specifically noted otherwise.
For purposes of power saving, IEEE 802.16-2005 (see particularly section 6.3.21) defines a sleep mechanism, which can be used to reduce the duty cycle during which a mobile station (MS) must listen for downlink signals. To invoke the mechanism, the MS transmits a sleep request (SLP-REQ) signal to the base station, identifying the frames during which the MS will be sleeping and will therefore not receive downlink signals. During these sleep frames, the MS may shut down some of its circuits and thus reduce power consumption without risk of missing a downlink transmission.